1. Field of the Invention
The invention relates generally to the field of fracturing subterranean formations. More specifically, the present invention relates to a method and apparatus of fracturing subterranean formations with a self-contained system disposable within a wellbore. The present invention involves a method and apparatus for fracturing using ultra-high pressure fluids. Though the subject invention has many uses, one of its primary uses is to fracture a subterranean formation within a well for stimulation of production in that well.
2. Description of Related Art
Stimulating the production of hydrocarbons from within hydrocarbon bearing subterranean formations is often accomplished by fracturing portions of the formation to increase fluid flow from the formation into a wellbore. Fracturing the formation, a process also known as fracing, typically involves sealing off or isolating a portion of the wellbore from the surface and pressurizing the fluid within the isolated portion of the wellbore to some pressure that in turn produces a fracture in the formation. The fluid being pressurized can be a drilling fluid, but can also be a fracturing fluid specially developed for fracturing operations. Examples of fracturing fluids include gelled aqueous fluids that may or may not have suspended solids, such as proppants, included within the fluid. Also, acidic solutions can be introduced into the wellbore prior to, concurrent with, or after fracturing. The acidic solutions can etch out fracture faces on the inner circumference of the wellbore that help to help create and sustain flow channels within the wellbore for increasing the flow of hydrocarbons from the formation.
The isolation of the wellbore prior to fracturing is performed either when using a gelled fluid as well as an acidic solution. Isolating the wellbore can be accomplished by strategically inserting a packer within the wellbore for sealing the region where the fluid is to be pressurized. Optionally, in some formations, a high-pressure fluid can be pumped into the wellbore thereby pressurizing the entire wellbore without isolating a specific depth within the wellbore for fracing. Examples of these methods can be found in the following references: U.S. Pat. No. 6,705,398, U.S. Pat. No. 4,887,670, and U.S. Pat. No. 5,894,888.
However one of the drawbacks of the presently known systems is that the fluid is dynamically pressurized by devices that are situated above the wellbore entrance. This requires some means of conveying the pressurized fluid from the pressure source to the region within the wellbore where the fluid is being delivered. Often these means include tubing, casing, or piping through which the pressurized fluid is transported. Due to the substantial distances involved in transporting this pressurized fluid, large pressure drops can be incurred within the conveying means. Furthermore, there is a significant capital cost involved in installing such a conveying system. Accordingly there exists a need for a fracturing system capable of directing pressurized fluid to an isolated zone within a wellbore, without the pressure losses suffered by currently known techniques.